1. Field of the Invention
The present invention relates to an exhaust gas recirculation (EGR) system for an internal combustion engine and, more particularly, to an exhaust gas recirculation (EGR) system so adapted as to recirculate a portion of exhaust gases into an intake system of the internal combustion engine.
2. Description of Related Art
Internal combustion engines, particularly for automotive vehicles, are designed such that a portion of exhaust gases is recirculated into the intake system. In other words, for example, as shown in Japanese Patent Publication No. 160,052/1984, the internal combustion engines adopt a so-called EGR system that has been employed as measures against NOx (measures to curtail NOx as hazardous ingredients in exhaust gases) in a light load region.
As effective means for enhancing heat efficiency of the internal combustion engine, it is known to set a compression ratio of the internal combustion engine to a high value. A supercharged engine is further known, which has a supercharger mounted to an intake system of the internal combustion engine so as to produce a large output at a small displacement. For the internal combustion engines of the type having a high compression ratio or the supercharged engines, the problems exist, first, in the fact that knocking is likely to occur in a high load region and, secondly, in the fact that heat load within the internal combustion engine or within the exhaust system thereof increases in the high load region. These problems make it difficult to set a high compression ratio. This is particularly so for the supercharged engines.